Which of the following is an example of a force? A. electrons moving toward a positive charge B. a child kicking a soccer ball C
2 answers:
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a) The work done is 920 J
b) The work done is 5200 J
Explanation:
a)
In this first part of the problem, the crate is moved horizontally at constant speed.
The work required in this case is given by
where
F is the magnitude of the force applied
d is the displacement of the crate
is the angle between the direction of the force and of the displacement
Here the crate is moved at constant speed: this means that the acceleration of the crate is zero, and so according to Newton's second law, the net force on the crate is zero: this means that the force applied, F, must be equal to the force of friction (but in opposite direction), so
F = 230 N
The displacement is
d = 4.0 m
And the angle is , since the force is applied horizontally. Therefore, the work done is
b)
In this case, the crate is moved vertically. The force that must be applied to lift the crate must be equal to the weight of the crate (in order to move it a constant speed), therefore
F = W = 1300 N
The displacement this time is again
d = 4.0 m
And the angle is , since the force is applied vertically, and the crate is moved also vertically. Therefore, the work done on the crate this time is
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The "penetration of the bullet" is 5 m
<u>Explanation</u>:
A "bullet" with "kinetic energy" of = 400J
A resistive force stops the bullet = 8.00 x 10 N
Work = change in energy
Work = ∆ Kinetic Energy (equation 1)
Work = (equation 2)
From equations 1 and 2 we have,
= ∆ Kinetic Energy
Where ,
Kinetic Energy = 400 J
F = 8.00 x 10 N
(8.00 x 10 N) d = 400 J
(80 N) d = 400 J
d = 5 m
The penetration of the bullet is 5 m